Sensory processing sensitivity (SPS), a personality trait, a high measure of which defines a highly sensitive person (HSP),[1][2] has been described as having hypersensitivity to external stimuli, a greater depth of cognitive processing, and high emotional reactivity.[1] The terms SPS and HSP were coined in the mid-1990s by psychologistsElaine Aron and husband Arthur Aron, with SPS being measured by Aron's Highly Sensitive Person Scale (HSPS) questionnaire.[1] Other researchers have applied various other terms to denote this responsiveness to stimuli that is evidenced in humans and other species.[3]

According to the Arons and colleagues, people with high SPS comprise about 15–20% of the population and are thought to process sensory data more deeply due to the nature of their central nervous system.[2] Although many researchers consistently related high SPS to negative outcomes,[1][4] Aron and colleagues state that high SPS is a personality trait and not a disorder;[5] other researchers have associated it with increased responsiveness to both positive and negative influences.[6][7][8][9]

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Elaine Aron's 1996 book The Highly Sensitive Person[10] defined a population of people having "increased sensitivity to stimulation" and who "are more aware of subtleties and process information in a deeper, more reflective way."[11] In 1997 Elaine and Arthur Aron formally identified[12]sensory processing sensitivity (SPS), the scientific term for highly sensitive or hypersensitivity,[2] as the defining trait of highly sensitive persons (HSPs).[1] By way of definition, Aron & Aron (1997) wrote that sensory processing here refers not to the sense organs as such, but to what occurs as sensory information is transmitted to or processed in the brain.[12] The trait has been described as "neither flaw nor gift, ... an amplifier of an environment's effects."[13]

Aron's professional journal articles and self-help publications have focused on distinguishing high SPS from socially reticent behavior[14] and disorders[15] with which high SPS can be confused;[16] overcoming the social unacceptability that can cause low self-esteem;[16] and emphasizing the advantages of high SPS[17] to balance the disadvantages emphasized by others.[4][16][18]

In 2015 Elizabeth Bernstein wrote in The Wall Street Journal that HSPs were "having a moment," noting that several hundred research studies had been conducted on topics related to HSPs' high sensitivity, and that a First International Scientific Conference on High Sensitivity or Sensory Processing Sensitivity had been held at the Vrije Universiteit Brussel.[19] By 2015, more than a million copies of The Highly Sensitive Person had been sold.[20]

Boterberg et al. (2016) describe high SPS as a "temperamental or personality trait which is present in some individuals and reflects an increased sensitivity of the central nervous system and a deeper cognitive processing of physical, social and emotional stimuli".[2]

People with high SPS report having a heightened response to stimuli such as pain, caffeine, hunger, and loud noises.[4] According to Boterberg et al., these individuals are "believed to be easily overstimulated by external stimuli because they have a lower perceptual threshold and process stimuli cognitively deeper than most other people."[2] This deeper processing may result in increased reaction time as more time is spent responding to cues in the environment, and might also contribute to cautious behavior and low risk-taking.[2]

The HSP Scale, initially (1997) a questionnaire designed to measure SPS on a unidimensional scale, was subsequently decomposed into two,[21][22] three,[23] or four[24] factors or sub-scales.[2] Most components have been associated with traditionally-accepted negative psychological outcomes[1][2] including high stress levels; being easily overwhelmed; increased rates of depression, anxiety, and symptoms of autism; sleep problems; and more physical health problems;[2] the diathesis-stress model focused on increased vulnerability to negative influences.[6] However, the differential susceptibility theory (DST)[6][7] and biological sensitivity to context theory (BSCT)[8] and sensory processing sensitivity (SPS)[25] suggest increased plasticity (responsiveness) to both positive and negative influences; and the vantage sensitivity (VS) concept emphasizes increased responsiveness to positive experiences.[9][26] Smolewska et al. (2006) said that in their research, positive outcomes were more common in individuals with high aesthetic sensitivity, who tend to experience heightened positive emotions in response to rewarding stimuli and more likely to score high on "openness" on the Big Five factors model.[27]

Research in evolutionary biology provides evidence that the trait of SPS can be observed, under various terms, in over 100 nonhuman species,[2][3] Aron writing that the SPS trait is meant to encompass what personality psychologists have described under various other names.[28] Conversely, Aron has distinguished SPS from what she considers it is not, explicitly distinguishing[29] high SPS from possibly-similar-appearing traits or disorders (such as shyness,[30] sensation-seeking,[31] sensory processing disorder,[15] and autism[5]), and further, that SPS may be a basic variable that may underlie multiple other trait differences[12] (such as introversion versus extraversion[29]).

Within humans and other species, two subpopulations of individuals persistently coexist and consistently display different levels of responsiveness to environmental stimuli; the subpopulations respectively embody "responsive" and "unresponsive" strategies that each have corresponding evolutionary costs and benefits.[3] This observation parallels Aron's assertion that high SPS is not a disorder, but rather a personality trait with attendant advantages and disadvantages.[5]

By 2015 the trait had been documented at various levels of study, including temperament and behavior (personality psychology), brain function and neuronal sensitization, and genetics.[7] For example, genetic studies provide evidence that higher levels of SPS are linked to the serotonin transporter5-HTTLPR short/short genotype,[32] polymorphisms in dopamine neurotransmitter genes,[33] and the ADRA2bnorepinephrine-related gene variant.[34]

HSP Scale score patterns in adults were found to be distributed as a dichotomouscategorical variable with a break point between 10% and 35%, with Aron choosing a cut-off of the highest-scoring 20% of individuals to define the HSP category.[2]

^Bartz, Andrea (July 5, 2011). "Sense and Sensitivity". Psychology Today. Archived from the original on May 12, 2016. Last reviewed: June 9, 2016. "... the double-edged nature of sensitivity. Neither flaw nor gift, it is, rather, an amplifier of an environment's effects."